Kemik Sandstone: Inner Shelf Sand from Northeast Alaska
The upper Neocomian Kemik Sandstone crops out in and around Ignek Valley in northeast Alaska. It lies unconformably on the Jurassic to Lower Cretaceous Kingak Shale, and is overlain by the Hauterivian to Barremian Pebble shale. It is a fine-grained, glauconitic quartzose sandstone, up to 120 ft thick. Four lithofacies are recognized: (1) a basal, moderately well-sorted pebble conglomerate; (2) fine to very fine-grained, laminated and bioturbated sandstones; (3) a poorly sorted conglomerate; and (4) low-angle to hummocky cross-stratified fine-grained sandstones. Facies relationships suggest that the basal conglomerate represents a transgressive lag deposit. It is overlain by a sequence comprising laminated and bioturbated sandstones with interbedded, poorly sorted conglome ates. The sandstones exhibit a mixed assemblage of ichnofossils, including Gyrochorte, Muensteria, Ophiomorpha, Planolites, Skolithos, and (?)Conichnus. In places, they grade upward from low-angle laminations to symmetrical ripple forms to silty laminated deposits. Their upper parts are bioturbated, but to varying extent. These sandstones and the conglomerates were deposited abruptly but sporadically below storm wave base by storm-generated currents. The sandstones were subsequently modified by strong but waning oscillating storm waves. The hummocky cross-stratified sediment comprises an upper sequence that was probably deposited under the influence of storm-induced conditions between fair-weather and storm wave base. The Kemik Sandstone represents a storm-deposited inner shelf sand with regressive characteristics, deposited within an overall transgressive setting.
AAPG Search and Discovery Article #91043©1986 AAPG Annual Convention, Atlanta, Georgia, June 15-18, 1986.